Extrusion



Nov. 1, 1938. J MQORHEAD 2,135,193 I EXTRUSiON Filed April 12, 19:55

INVENTO'R N .foscp/i mar/764a A ATTORNEY Patented Nov. 1, 1938 UNITED"STATES EXTBUSION Joseph N. Moor-head, Shaker Heights, Ohio, as-

signor to Aluminum Company of America, Pittsburgh, Pa", a corporation ofPennsylvania Application April 12, 1935, Serial Na. 15,931

3 Claims.

This invention relates to improvements in extrusion of metals and isparticularly directed towards the extrusion of non-ferrous metals suchas aluminum and its alloys.

In the extrusion of metals, wherein a heated metal billet, suitablyconfined, is expressed in indefinite lengths through a die orifice ofdesired configuration, there are certain factors which control the speedat which the metal may be extruded. Among these factors, which arenumerous, are the friction presented by the bearing surface of a dieconfiguration, the temperature of the particular metal being extruded,and the pressure applied on the billet or charge essential 1 to extrudethe same. All of these factors militate against the speed at which anymetal may be extruded, in that they are responsible for a phenomenonknown as "pick-up", which is defined herein as that metal and/or oxideof the charge being extruded which adheres or bonds, as by a welding oralloying action, to the bearing surface of an extrusion die. v

Pick-up varies in amount in accordance with the characteristics of theparticular metal being extruded, in that each metal and its alloysrequires a definite temperature to which it must be heated prior toitsextrusion. Likewise, the die orifice configuration and the pressureessential to extrude a metal also react in the generation of heat byfriction. The heat thus generated and the extreme pressures under whichmetals are extruded react to increase the bonding action between themetal of a billet and an extrusion die, and the pick-up thus formedonthe bearing surface of the die greatly impairs the speed at which ametalmay be extruded.

The factors of temperature and pressure, which greatly influence theformation of pick-up, are accentuated by the particular configuration 40of the extrusion die for any given extruded shape. In simple dies, suchas a circular orifice, the amount of pick-up is much less than thatwhich would result in the use of an intricate die orifice having angularfaces and otherwise presenting a complicated structure susceptible toincreasedfriction and increased pressure necessay to cause metal to flowtherethrough.

The disadvantages above referred to exist in known extrusion practice,although it has been known to lubricate dies with fluids in an attemptto remedy these disadvantages. The lubrication procedures in use,however, have failed to relieve the pick-up condition existing in normalextrusion operations, and the speeds under which metals arenow beingextruded are relatively slow and add greatly to the cost of extrudedmaterials.

It is an object of the present invention to provide a process which willpermit speeds of extrusion which have heretofore never been attained. Itis also an object of the invention to provide a processwhich readilyadapts itself to knownextruslon apparatus and is effective in producinga more economic product than heretofore possible. Otherobjects andadvantages will present 1 themselves on further consideration of thespecification.

It has now been discovered that the die temperature is -the only factorinvolved in the formatlon of pick-up which may be satisfactorily con- 1trolled, and means have been provided whereby the die temperature isclosely controlled. In obtaining relief from pick-up thespeed ofextrusion is automatically increased,and the interruptions heretoforenecessary for the cleaning, 20 polishing, or otherwise removing pick-upfrom extrusion dies, have been eliminated, thereby increasing theproductive output of extrusion mechanisms.

In the practice of the invention the main dea sideratum is thesubstantial elimination of pickup on extrusion die bearing surfaces. Inobtaining this condition it is now found that, if the temperature of anextrusion die is maintained at a temperature lower than that at whichthe metal being extruded therethrough will bond or otherwise weld to thedie bearing surface under the influence of the temperature and pressureemployed, substantially no pick-up will accumulate on the die bearingsurface. This condition is obtained through the medium of any suitablecooling medium applied adjacent the die bearing surface. In most cases,water, a readily available coolant, has been considered preferable inthe application of this invention, but, manifestly, 3: other coolingmedia may be employed.

In the simplest form of the invention, water is sprayed directly uponthe extrusion die adjacent the metal exuding therefrom, the amount ofwater being so controlled that the heat generated 5 by the extrusionoperation, andits related temperature-raising factors, is dissipated toadegree at which the metal of the billet will not bond or otherwiseadhere to the bearing surface of the die. More complicated designs ofextrusion 5o equipment will manifestlynecessitate a particular means forapplying the cooling medium, such means usually depending upon theaccessibility of the die in a particular apparatus being used, and insuch cases it is sometimes necessary to u resort to internal cooling ofan extrusion die. However, such instances do not offer any impediment inthe practice of the invention, it being the chief requirement forthesuccess of the present invention that the die be maintained below thetemperature at which the metal being extruded will bond or otherwiseweld to the die bearing surface at any time during the extrusionoperation.

Exemplary of actual practice, as applied to the' extrusion of analuminum alloy having the approximate composition, 97.5 per centaluminum, 0.7 per cent silicon, 1.3 per cent magnesium, 0.25 per centchromium, and 0.25 per cent maximum impurities, it has been found that,for proper extrusion conditions, the billet should be initially' heatedto between about 750 to 800 Fahrenheit. Extruding this preheated billetin the usual manner an extrusion speed of to 50 feet per minute wasreached before the product commenced to show a roughened surface causedby pick-up. A similar billet preheated to the same temperature andextruded through the same die, cooling water being supplied insufilcient quantity to maintain the die at a temperature lower than thatreached by the billet at any time during the extrusion thereof,permitted a speed of 150 feet per minute to be attained without in anyway indicating an impaired surface. It was also noted during theextrusion operation above referred to that the temperature of theextruded product reached a maximum of 970 Fahrenheit, which isindicative of the heat generated during an extrusion operation, and thephysical properties of the product produced at the higher extrusionspeed, with water-cooled die, were appreciably higher than theproperties of the product produced in the usual method of extrusion.

It will be manifest, then, that the water cooling step, whereby heatgenerated at an extrusion die is dissipated, has resulted in an improvedprocess of extrusion, and although the example herein given is confinedto a particular alloy composition, the invention is equally adaptable toother metals and their alloys, the main desideratum being maintainingthe die temperav ture lower than that at which the metal being extrudedwill bond or otherwise adhere to the die bearing surface under thepressures used to extrude the particular metal.

In order that a more thorough understanding of the invention may be had,reference is made to the drawing accompanying this specification andforming a part thereof, in which:

Fig. 1 represents a fragmentary sectional elevation through the forwardor die end of an extrusion press;

Fig. 2 represents a view of the mechanism shown in Fig. 1 and takenalong the line 11-11 thereof; and v Fig. 3 represents an enlargedfragmentary view in partial sectional elevation illustrating the coolingsystem adjacent the die and back-up member.

Referring in particularity to the drawing, wherein the various elementsof the apparatus are identified by reference numerals, I represents thepress head or platen of a horizontal extrusion press, said head beingsuitably tied into a pressure cylinder supporting member, not shown,

The tool container bracket 3 is provided with an open top bore 5 intowhich a die and back-up adapter ring 6 concentrically fits, said member6 being formed with an interior bore to retain a die I and back-upmember 8, the die and ring being shown in sectional elevation in Fig. 1.A locking ring 9, engaged within concentric keyways in the adapter ring6 and bracket 3, retains the adapter ring 6 within the bore 5, andfiller members or rings H), H, II complete the tool assembly. Analternative construction for looking ring 9, which has been foundsatisfactory, comprises forming the ring 9 as a web or rib integralwith, and extending inwardly into, the bore 5 of bracket 3.

A fragmentary portion of abillet container cylinder I2 is shown abuttingagainst the tool assembly in operating position, said cylinder beingmounted in any suitable manner for reciprocating movement towards andaway from the die.

The description of the mechanism thus far is representative of astandard form of extrusion apparatus, andin order that the same may beoperated in accordance with thepresent invention, channels H areprovided in the interior bore of theadapter ring 6 for the purpose ofcirculating a suitable cooling medium therethrough. Fig. 3 illustrates,to an enlarged scale, the preferred disposition of the channels it,wherein they are illustrated as being disposed adjacent the die 1 andback-up member 8. The channels H are suitably interconnected and acooling medium supply pipe l5 and drain pipe l6 complete a continuoussystem for providing sumcient coolant to maintain the die at atemperature lower than that reached by the metal to be extruded.

In operation, the particular pressure required to extrude a particularmetal through a given die orifice is first determined by experiment, theinitial temperature of the billet having likewise been determined forproper extrusion characterististics. Knowing the pressure and initialtemperature, the temperature to which the die will be raised during thesubsequent extrusion operation may be approximated, and sufllcientcoolant is then supplied to the inlet pipe l5 to insure a dietemperature satisfactory to insure against the formation of pick-up. Thecoolant may be regulated during the extrusion operation, as isusually'the preferred practice, since the die temperature increases withthe duration of the extrusion operation. Furthermore, it is preferredthat the cooling medium be applied or introduced to thedie immediatelyfollowing the actual start of an extrusion operation, the

application of the coolant to continue for the duration of the extrusionoperation. This method of controlling the coolant insures against anypossibility of the cooling medium entering the billet cylinder, throughthe die, into contact with a heated billet, which action is susceptibleof serious consequences resulting from the generation of steam withinthe billet cylinder.

Although the invention has been described in particularity with respectto a single type of extrusion press and a definite alloy composition, itis to be understood that the invention is in no way limited in theserespects, but is applicable broadly asdefined in the appended claims.

What is claimed is:

1. The method of eliminating pick-up on an extrusion die in theextrusion of aluminum and its alloys, comprising heating a solid billet.of the metal and expressing the heated solid billet through said die,and cooling said die during the extrusion operation, said cooling beingregulated to maintain the die temperature below that reached by thebillet during all stages in its extrusion.

2. The method of extruding aluminum and aluminum alloys free fromlongitudinal surface grooves and other surface defects caused bypick-up, which comprises the steps, heating a solid billet of the metaland expressing it through an extrusion die, and cooling said die duringthe extrusion operation, said cooling being regulated to maintain thedie temperature below that reached by the billet during all stages inits extrusion.

3. The method of extruding aluminum and aluminum alloys free fromlongitudinal surface grooves and other surface defects caused bypick-up, which comprises the steps, heating a solid billet of the metaland expressing it through an extrusion die, and supplying coolant tosaid die in sufficient quantity to maintain its temperature lower thanthat reached by the billet during all stages in its extrusion.

JOSEPH a. MOORHEAD.

